There are many street food, market and restaurant sell northern Thai food in Chiang Mai. Some of them are good and some are not. These are some restaurant I recommend if you are interested in northern Thai food.

By ThaiCooking ChiangMai

HUEN PHEN เฮือนเพ็ญ (Old city area)

A long run and famous northern Thai food restaurant since I was child. Taste is authentic in a reasonable price 30-50 Baht for a normal dish.